1. Field of the Invention
This invention relates to novel dye precursor compounds, to certain metal complexes thereof and to a method of synthesizing certain of the dye precursor compounds.
2. Background Art
Gilman, Henry, Organic Chemistry, An advanced Treatise, Vol. III, John Wiley & Sons, New York, 1953, pp. 247-55 reviews organic dyes including the general concepts of, and early and modern theory regarding the relationship between color and chemical constitution. As discussed therein, a chromophore called a chromogene may be colored but does not yet represent a dye. To achieve this a further introduction of salt-forming groups, "auxochromes", into the molecule is required. The function of chromophore and auxochrome groups according to modern theory is necessary for modifying the molecule so as to introduce the possibility of resonance and thus color.
Although 3,3-disubstituted thiophthalides and dithiophthalides have been disclosed previously, none of the triarylmethane compounds described are dye precursors, i.e., color formers, since they do not exhibit the color-forming properties of dyes. In particular, R. Meyer, Ber. 33, pp. 2570-2576 and R. Meyer and J. Szanecki, ibid, pp. 2577-2583 disclose the synthesis of 3 3-dithiofluorane, dithiophenylphthalide (3,3-diphenylthiophthalide) and dithiodichlorofluorane by fusing the corresponding phthalides with phosphorus pentasulfide. The 3.3-dithiofluorane and the dithiodiphenylphthalide lack the auxochromic substituents necessary to complete the auxochromophoric system of a triarylmethane dye. The dithiodichlorofluorane also does not exhibit the properties of a dye, presumably because the chloro groups are not providing an auxochromic effect.
I. P. Soloveichik, et al., Zhurnal Organicheskoi Khimii, Vol. 10, No. 3, pp. 615-618, March, 1974 disclose the preparation of 3,3-diphenylthiophthalide by reacting the 3,3-diphenyldithiophthalide of Meyer and Szanecki with mercuric acetate and also by reacting o-benzoylbenzoic acid and phosphorus pentasulfide followed by phenylation with the Friedel-Crafts reaction as previously described by I. O'Brochta, et al., J. Am. Chem. Soc., 61, 2762 (1959). U.S. Pat. No. 2,097,435 discloses a synthesis for thiophthalides including 3,3-diphenylthiophthalide by reacting the corresponding phthalide with sodium hydrosulfide under anhydrous conditions in the absence of air or oxygen. Like the 3,3-diphenyldithiophthalide discussed above, 3,3-diphenylthiophthalide is not a dye precursor since the 3,3-phenyl moieties lack an auxochromic substituent to impart dye properties.